Details: 63 individuals were randomized to either a low-fat diet group, or a low-carb diet group. The low-fat group was calorie restricted. This study went on for 12 months.

Weight Loss: The low-carb group lost more weight, 7.3% of total body weight, compared to the low-fat group, which lost 4.5%. The difference was statistically significant at 3 and 6 months, but not 12 months.

Conclusion: There was more weight loss in the low-carb group, significant at 3 and 6 months, but not 12. The low-carb group had greater improvements in blood triglycerides and HDL, but other biomarkers were similar between groups.

Details: 132 individuals with severe obesity (mean BMI of 43) were randomized to either a low-fat or a low-carb diet. Many of the subjects had metabolic syndrome or type II diabetes. The low-fat dieters were calorie restricted. Study duration was 6 months.

Weight Loss: The low-carb group lost an average of 5.8 kg (12.8 lbs) while the low-fat group lost only 1.9 kg (4.2 lbs). The difference was statistically significant.

Conclusion: The low-carb group lost significantly more weight (about 3 times as much). There was also a statistically significant difference in several biomarkers:

Triglycerides went down by 38 mg/dL in the LC group, compared to 7 mg/dL in the LF group.

Insulin sensitivity improved on LC, got slightly worse on LF.

Fasting blood glucose levels went down by 26 mg/dL in the LC group, only 5 mg/dL in the LF group.

Insulin levels went down by 27% in the LC group, but increased slightly in the LF group.

Overall, the low-carb diet had significantly more beneficial effects on weight and key biomarkers in this group of severely obese individuals.

Details: 30 overweight adolescents were randomized to two groups, a low-carb diet group and a low-fat diet group. This study went on for 12 weeks. Neither group was instructed to restrict calories.

Weight Loss: The low-carb group lost 9.9 kg (21.8 lbs), while the low-fat group lost 4.1 kg (9 lbs). The difference was statistically significant.

Conclusion: The low-carb group lost significantly more (2.3 times as much) weight and had significant decreases in Triglycerides and Non-HDL cholesterol. Total and LDL cholesterol decreased in the low-fat group only.

Details: 53 healthy but obese females were randomized to either a low-fat diet, or a low-carb diet. Low-fat group was calorie restricted. The study went on for 6 months.

Weight Loss: The women in the low-carb group lost an average og 8.5 kg (18.7 lbs), while the low-fat group lost an average of 3.9 kg (8.6 lbs). The difference was statistically significant at 6 months.

Conclusion: The low-carb group lost more weight (2.2 times as much) and had significant reductions in blood triglycerides. HDL improved slightly in both groups.

Details: A randomized, crossover trial with 28 overweight/obese individuals. Study went on for 30 days (for women) and 50 days (for men) on each diet, that is a very low-carb diet and a low-fat diet. Both diets were calorie restricted.

Weight Loss: The low-carb group lost significantly more weight, especially the men. This was despite the fact that they ended up eating more calories than the low-fat group.

Conclusion: The low-carb group lost more weight. The men on the low-carb diet lost three times as much abdominal fat as the men on the low-fat diet.

Details: 102 patients with Type 2 diabetes were randomized to a low-carb or a low-fat diet for 3 months. The low-fat group was instructed to reduce portion sizes.

Weight Loss: The low-carb group lost 3.55 kg (7.8 lbs), while the low-fat group lost only 0.92 kg (2 lbs). The difference was statistically significant.

Conclusion: The low-carb group lost more weight and had greater improvements in the Total cholesterol/HDL ratio. There was no difference in triglycerides, blood pressure or HbA1c (a marker for blood sugar levels) between groups.

Conclusion: The Atkins group lost the most weight, although the difference was not statistically significant. The Atkins group had the greatest improvements in blood pressure, triglycerides and HDL. LEARN and Ornish (low-fat) had decreases in LDL at 2 months, but then the effects diminished.

Details: 13 diabetic and 13 non-diabetic individuals were randomized to a low-carb diet or a "healthy eating" diet that followed the Diabetes UK recommendations (a calorie restricted, low-fat diet). Study went on for 3 months.

Weight Loss: The low-carb group lost 6.9 kg (15.2 lbs), compared to 2.1 kg (4.6 lbs) in the low-fat group.

Conclusion: The low-carb group lost more weight (about 3 times as much). There was no difference in any other marker between groups.

Details: 107 individuals with abdominal obesity were randomized to a low-carb or a low-fat diet. Both groups were calorie restricted and the study went on for 8 weeks.

Weight Loss: The low-carb group lost 7.9% of body weight, compared to the low-fat group which lost 6.5% of body weight.

Conclusion: The low-carb group lost more weight and there was no difference between groups on Flow Mediated Dilation or any other markers of the function of the endothelium (the lining of blood vessels). There was also no difference in common risk factors between groups.

Details: 88 individuals with abdominal obesity were randomized to a very low-carb or a low-fat diet for 24 weeks. Both diets were calorie restricted.

Weight Loss: The low-carb group lost an average of 11.9 kg (26.2 lbs), while the low-fat group lost 10.1 kg (22.3 lbs). However, the difference was not statistically significant.

Conclusion: The low-carb group lost more weight. Triglycerides, HDL, C-Reactive Protein, Insulin, Insulin Sensitivity and Blood Pressure improved in both groups. Total and LDL cholesterol improved in the low-fat group only.

Details: 61 individuals with type 2 diabetes were randomized to a low-carb or a low-fat diet for 2 years. Both diets were calorie restricted.

Weight Loss: The low-carb group lost 3.1 kg (6.8 lbs), while the low-fat group lost 3.6 kg (7.9 lbs). The difference was not statistically significant.

Conclusion: There was no difference in weight loss or common risk factors between groups. There was significant improvement in glycemic control at 6 months for the low-carb group, but compliance was poor and the effects diminished at 24 months as individuals had increased their carb intake.

3

Weight Loss

21 of 23 studies reported weight loss numbers.

The majority of studies achieved statistically significant differences in weight loss (always in favor of low-carb). There are several other factors that are worth noting:

The low-carb groups often lost 2-3 times as much weight as the low-fat groups. In a few instances there was no significant difference.

In most cases, calories were restricted in the low-fat groups, while the low-carb groups could eat as much as they wanted.

When both groups restricted calories, the low-carb dieters still lost more weight (7, 13, 19), although it was not always significant (8, 18, 20).

There was only one study where the low-fat group lost more weight (23) although the difference was small (0.5 kg - 1.1 lb) and not statistically significant.

In several of the studies, weight loss was greatest in the beginning. Then people start regaining the weight over time as they abandon the diet.

Two of the main reasons why low-carb diets are so effective for weight loss are the high protein content, as well as the appetite-suppressing effects of the diet. This leads to an automatic reduction in calorie intake.

LDL Cholesterol

Despite the concerns expressed by many people, low-carb diets generally do not raise Total and LDL cholesterol levels on average.

Low-fat diets do lower Total and LDL cholesterol, but it is usually only temporary. After 6 to 12 months, the difference is not statistically significant.

There have been some anecdotal reports by doctors who treat patients with low-carb diets, that they can lead to increases in LDL cholesterol and some advanced lipid markers for a small percentage of individuals.

However, none of the studies above noted such adverse effects. The few studies that looked at advanced lipid markers (5, 19) only showed improvements.

5

HDL Cholesterol

One of the best ways to raise HDL cholesterol levels is to eat more fat. For this reason, it is not surprising to see that low-carb diets (higher in fat) raise HDL significantly more than low-fat diets.

Having higher HDL levels is correlated with improved metabolic health and a lower risk of cardiovascular disease. Having low HDL levels is one of the key symptoms of the metabolic syndrome.

18 of the 23 studies reported changes in HDL cholesterol levels.

You can see that low-carb diets generally raise HDL levels, while they don't change as much on low-fat diets and in some cases go down.

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6

Triglycerides

Triglycerides are an important cardiovascular risk factor and another key symptom of the metabolic syndrome.

The best way to reduce triglycerides is to eat less carbohydrates, especially sugar.

19 of 23 studies reported changes in blood triglyceride levels.

It is clear that both low-carb and low-fat diets lead to reductions in triglycerides, but the effect is much stronger in the low-carb groups.

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7

Blood Sugar, Insulin Levels and Type II Diabetes

In non-diabetics, blood sugar and insulin levels improved on both low-carb and low-fat diets and the difference between groups was usually small.